Frequently, it is desired to form amorphous masses of material into end products of predetermined shape and thickness, utilizing machinery which affords substantial uniformity, speed and ease. Thus, for example, food products, such as tortillas, may be formed from dough made from corn flour, in the shape of circles of substantially uniform thickness. Traditionally, various methods have been utilized for producing such products, from the hand formation of individual pieces, to die-cutting from flat-rolled sheets. It has also been proposed to extrude dough into such desired shapes, utilizing a slot-like aperture on an extruder in conjunction with an associated cutting valve. The latter may be in the form of a cylinder having a configured portion which remains after removing part of the shell of the cylinder. As the cylinder revolves while positioned in the aperture slot, the amount, dimensions and configuration of the dough which the extruder is permitted to force through the slot may thereby be governed. In this connection, reference is made to Emerzian U.S. Pat. No. 2,981,211. However, in actual practice, it has been found that such devices do not produce products exhibiting the desired degree of uniformity, size and configuration, particularly as attempts are made to increase production speeds and output. For example, it has been found that such devices, designed to produce circular pieces of substantially uniform thickness, tend, particularly as it is attempted to increase the amount of production, to produce items which are more teardrop in shape, with wider leading portions and narrower trailing portions, and with the leading portion thicker than the trailing portion. Without intending to be bound by any theory, it is believed that these undesirable results may be rationalized by considering the various phenomena which are believed to come into play in such operations. First, it will be seen that in such devices designed to produce circular pieces, because of the physical relationship between the retained portions of the cylinder shell and the associated slotted extrusion aperture as the former rolls within the latter, the slot "sees" a gate which opens progressively toward the slot ends from the center, and then reverses the process. Assuming a constant rate of pressure being applied to the dough within the apparatus, it will be seen that the pressure will have built up on the somewhat plastic dough during the time when the extrusion slot is totally covered by the web portion of the cylinder shell. As the web passes the slot and the gate begins to open, the amount of dough extruded through the slot, being a function of the pressure being applied to the dough, will be higher than it is later on in the sequence when the widest part of the cylinder shell has passed the aperture, causing the extruded shape to be thicker and wider because of the comparative excess of dough material being presented. Thereafter, the pressure of the dough may increase somewhat due to the progressive closure of the valve, but not to the level it reaches upon the valve first opening, after having been closed for a time as the web portion passes the extrusion slot. Correspondingly, as the aperture commences closing after passing the widest "open" position, the pressure on the dough then being lowest, the extruded form will tend not to be so thick, or to be filled out as widely in the lateral dimensions. Thus, the conditions are present to produce a final shape which is not of desired uniformity in thickness or in circumferential configuration. Experience shows that such undesired results may be further aggravated where the work product is extruded onto an associated conveyor belt or other transport means to remove the extruded product. Apparently, when such a belt is traveling at a substantially uniform speed, the excess extrusion at the beginning of each cycle is not carried away rapidly enough by the belt, which tends to make the work product "fatter" in thickness and width at the front, but "thinner" in thickness and width at the rear when the belt, although still moving forward at a constant speed, is moving too fast for the volume of extruded material which has by then been decreased. These undesired results have been found to become progressively more severe as it is attempted to increase production with such devices by speeding them up. Again, without intending to be bound by any theory, it is believed this may be due to the necessity, with such attempts to speed-up, to increase correspondingly, the basic extrusion pressure on the dough, with resulting wider ranges in the pressure which the dough exhibits toward extrusion as the valve goes through its successive cycles.
Attempts to use an extrusion aperture in conjunction with a cylinder having a surface depression, to form a forming die (as contrasted with an extrusion cutting valve of the type hereinbefore described) in which the desired shape could be formed and then kept isolated from any subsequent effect of extrusion pressures on the raw material feed, present the technically difficult problem of removing the formed product. In this connection, reference is made to Atkins U.S. Pat. No. 3,541,974. There is illustrated a relatively complex, and therefore inherently more costly and slower, pneumatic stripper for a cylindrical dough die-forming device. Clearly, such apparatus is not satisfactory for high speed, accurate production, for example, in the production of food-products such as tortillas.
Accordingly, an object of the present invention is to provide means to produce desired products from plastic materials in a wide range of thicknesses within desired physical limits.
Another object of this invention is to provide such means to produce such products at a relatively high speed.
Still another object of this invention is to provide means within the contemplation of the foregoing objectives which are relatively simple to produce and operate.
Yet another object of this invention is to provide means within the contemplation of the foregoing objectives which is technically reliable to produce such products with acceptable parameters of dimensional and configurational uniformity.